Conventional grating structures can reflect light about a reflective axis that differs from surface normal of the medium in which the grating structure resides. However, for a given angle of incidence, angles of reflection for conventional grating structures typically covary with wavelength of incident light. Moreover, a conventional grating structure is typically limited to a single angle of incidence (or very narrow range of incidence angles), in order to reflect light of a specified wavelength about a constant reflective axis. Conventional grating structures may also diffract light of some polarization states more strongly than others, and some polarization states may not be diffracted at all. In some optical systems, light sources generate light with randomized polarizations. In these systems, conventional grating structures may waste much of the light and, therefore, may not be efficient in many beam redirection or light coupling applications.
Accordingly, requirements for an optical device including at least one light coupling element that manages the polarization of light to efficiently reflect light about a reflective axis not constrained to surface normal, and whose angle of reflection for a given angle of incidence is constant across a range of incidence angles, are not met by currently available devices comprising reflective grating structures. A need therefore exists for such an optical device that manages polarization of light and interactions of reflected light with one or more grating structures, and such need may be acute in head-mounted display (HMD) devices.